Partially crystalline state decomposition

Araujo-Andrade et al. reported an interesting investigation on (tetrazol-5-yl)-acetic acid (TAA). Monomers of the compound were obtained by sublimation and isolated in a N2 matrix at 13 K. In gas phase, TAA may adopt two tautomeric modifications, IH- and 2H-, depending on the position of the annular hydrogen atom (Fig. 7), but in the crystalline state only tautomer H- is present. Each of the tautomeric forms of TAA has several different possible conformers. In their study, Araujo-Andrade and coworkers presented a mechanistic explanation for the observed 1H- 2H tautomerization of TAA upon sublimation of the compound, and simultaneous partial decomposition into 5-methyl-tetrazole and CO2. Such mechanism implies the occurrence of a concerted proton transfer (O-H N) between vicinal TAA molecules along the molecular chains of the crystal, to form the 2Ff-tautomer and generate CO2 and 5-methyl-tetrazole at the crystal boundaries and crystal defects. A detailed characterization of the conformational and tautomeric compositions of... 

Quantitative evaluation of the 2D-HETCOR spectra are presented in Table 7.3. As expected incubation in r-SBF causes over time dissolution of phases characterised by the distorted states 1 and 2 associated with oxyhydroxyapatite, that is partially dehydroxylated SRO-structured hydroxyapatite as well as dissolution of the thermal decomposition products TTCP and TCP, but to a lesser extent. Concurrently the relative proportion of crystalline well-ordered hydroxyapatite increases from 46 mass% in an as-sprayed coating to 74 mass% in a coating incubated under physiological conditions for 12 weeks. 

For the hydroljdic decomposition the thallium ethoxide is cooled in an ice bath without separating excess alcohol (to prevent partial conversion of the TlOH to black TlgO) and treated with an equal volume of boiled and recooled distilled water. Alcohol is then evaporated in vacuum. Yellow, crystalline TlOH separates. DeForcrand states that the product still retains 4% moisture after 24 hours of standing in a desiccator on porous tile. 

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